More CI cleanup, add style workflow (#107)

- Changes on the `test.yml` workflow:
  - Using poetry instead of pip. Contrary to what I wrote in #75, it is possible to use poetry (and have the benefits of shorter install times) without the need for having two separate versions of `pyproject.toml` and `poetry.lock`.
  - Reduce the trigger scope to only run when files in these directories are modified:
    - `lerobot/`
    - `tests/`
    - `examples/`
    - `.github/`
- Add `style.yml` workflow for doing a `ruff check` pass on the code
- More cleanup (removed deprecated workflow)

pyproject.toml

@@ -68,6 +68,7 @@ test = ["pytest", "pytest-cov"]
 line-length = 110
 target-version = "py310"
 exclude = [
+    "tests/data",
     ".bzr",
     ".direnv",
     ".eggs",